Changes in salt marsh detritivore identity influences on ecosystem multifunctionality

Ecosystems world-wide experience changes in species composition in
response to natural and anthropogenic changes in environmental conditions.
 Research to date has greatly improved our understanding of how
species affect focal ecosystem functions.  However, because
measurements of multiple ecosystem functions have not been consistently
justified for any given trophic group, it is unclear whether
interpretations of research syntheses adequately reflect the contributions
of consumers to ecosystems.  Using model communities assembled in
experimental microcosms, we examined the relationship between four
numerically dominant detritivore species and six ecosystem functions that
underpin fundamental aspects of carbon and nitrogen cycling above- and
below-ground.  We tested whether ecosystem responses to changes
in detritivore identity depended upon species trait dissimilarity, food
web compartment (aboveground, belowground, mixed), or number of responses
considered (one to six). We found little influence of detritivore species
identity on brown (i.e. soil-based) processes.  Only one of four
detritivore species uniquely influenced decomposition, and detritivore
species did not vary in their influence on soil nitrogen pools (NO3- and
NH4+), or root biomass.  However, changes in detritivore identity
influenced multiple aboveground ecosystem functions.  That is, by
serving as prey, ecosystem engineers, and occasionally also as herbivores
as well as detritivores, these species altered the strength of aboveground
predator-herbivore interactions and plant-shoot biomass.  Yet,
dissimilarity of detritivore functional traits was not associated with
dissimilarity of ecosystem functioning.  These results serve as
an important reminder that consumers influence ecosystem processes via
multiple energy channels and that food web interactions set important
context for consumer-mediated effects on multiple ecosystem
functions.  Given that species are being lost, gained, and
redistributed at unprecedented rates, we can anticipate that changes in
species identity will have additional ecosystem consequences beyond those
predicted by species’ primary functional role.